Microelectromechanical systems (“MEMS”) are used in a growing number of applications. For example, MEMS are currently implemented as gyroscopes to detect pitch angles of airplanes, and as accelerometers to selectively deploy air bags in automobiles. In simplified terms, many such MEMS devices often have a structure suspended above a substrate, and associated circuitry that both senses movement of the suspended structure and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., pitch angle or acceleration).
Current accelerometers most typically are available in either a low G design that is optimized to sense low G acceleration, or a high G design that is optimized to sense high G acceleration. Due to the sensitivity and accuracy required, the low G accelerometers are typically designed to have a high resolution (e.g., 0.5 mg/LSB or lower), low noise (1 mg or lower), and excellent offset stability (<70 mg for the life of the product). Conversely, because high G accelerometers need to operate over a large range, they are typically designed to have a large detection range (e.g., up to 480G—far larger than low G accelerometers, such as 8 g or 16 g), and excellent overload performance (e.g., up to 1000 g for velocity preservation).
Prior art accelerometers have been unable to combine both low G and high G performance into a single accelerometer because of the inherent differences in design and performance requirements. For example, the high overload performance required for the high G accelerometer negatively impacts the high resolution required for the low G accelerometer.